Numerical simulation is already an important cornerstone for aircraft design, although the application of highly accurate methods is mainly limited to the design point. To meet future technical, economic and social challenges in aviation, it is essential to simulate a real aircraft at an early stage, including all multidisciplinary interactions covering the entire flight envelope, and to have the ability to provide data with guaranteed accuracy required for development and certification. However, despite the considerable progress made there are still significant obstacles to be overcome in the development of numerical methods, physical modeling, and the integration of different aircraft disciplines for multidisciplinary analysis and optimization of realistic aircraft configurations. At DLR, these challenges are being addressed in the framework of the multidisciplinary project Digital-X (4/ 2012-12/2015). This paper provides an overview of the project objectives and presents first results on enhanced disciplinary methods in aerodynamics and structural analysis, the development of efficient reduced order methods for load analysis, the development of a multidisciplinary optimization process based on a multi-level/variable-fidelity approach, as well as the development and application of multidisciplinary methods for the analysis of maneuver loads.
Suitable and fast calculation methods with sufficient accuracy are required to optimise large composite structures. The present paper introduces a progressive stiffness degradation analysis (PSDA), which computes skin buckling onset and strength failure initiation of skin fields separated by stiffeners, as well as the subsequent damage propagation using closed form solutions. This constitutes a simplified, but much faster approach compared to state of the art progressive failure analyses, which incorporate finite element simulations. Therefore, the computational effort can be reduced. This paper illustrates the process of the PSDA and then verifies this simplified approach by means of one example.
Purpose -To obtain a good start configuration in the early design phase, simulation tools are used to create a large number of product designs and to evaluate their performance. To reduce the effort for the model generation, analysis and evaluation, a design environment for thin-walled lightweight structures (DELiS) with the focus on structural mechanics of aircrafts has been developed. Design/methodology/approach -The core of DELiS is a parametric model generator, which creates models of thin-walled lightweight structures for the aircraft preliminary design process. It is based on the common parametric aircraft configuration schema (CPACS), which is an abstract aircraft namespace. DELiS facilitates interfaces to several commercial and non-commercial finite element solvers and sizing tools. Findings -The key principles and the advantages of the DELiS process are illustrated. Also, a convergence study of the finite element model of the wing and the fuselage and the result on the mass after the sizing process are shown. Due to the high flexibility of model generation with different levels of detail and the interface to the exchange database CPACS, DELiS is well suited to study the structural behaviour of different aircraft configurations in a multi-disciplinary design process. Originality/value -The abstract definition of the object-oriented model allows several dimensions of variability, such as different fidelity levels, for the resulting structural model. Wings and fuselages can be interpreted as finite beam models, to calculate the global dynamic behaviour of a structure, or as finite shell models.
In times of reducing product development cycles and greater economical, safety and ecological requirements on aircraft structures innovative aircraft configurations with new materials and new structural design concepts become more and more important. Although their positive impact on the conventional pre-design methods come to their limits and to an appropriate tools for design and evaluation the need for Multidisciplinary Design Optimization increases.. In this paper a structural design and optimization module developed for the application in such an optimization process is presented. The module is coupled to the software environment DELiS where structural models mathematically described by finite elements can be automatically created, based on a parametric description. The outer loads, coming from CFD or aeroelastic calculations, are applied to the model and inner loads are calculated utilizing a linear static finite element analysis. To evaluate the results information about inner loads, displacements, properties and geometry are passed to the commercial software tool HyperSizer. Material parameters like thickness and stacking sequence and also cross sectional stringer parameters are optimized for the given loads on panel level. For sizing and optimization a set of failure criteria is used; analytical equations are available for a reduced calculation time. The capabilities of the module and the sizing approach are demonstrated on a composite wing of a long range transport aircraft.
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